Methamphetamine use among HIV-positive men who have sex with men is associated with sub-optimal adherence, poor clinical outcomes, sexual risk-taking, and higher levels of life chaos. For these reasons, HIV- positive methamphetamine-using men who have sex with men (HIV+ MU-MSM) require antiretroviral therapy (ART) adherence interventions tailored to their unique context, concerns, and lifestyle. The overall aim of this project is to develop and assess the feasibility and acceptability of a smart phone application (app) ART adherence intervention tailored to the needs of HIV+ MU-MSM and grounded in an adapted version of the Information-Motivation-Behavioral Skills (IMB) model. Although much of the content within the core constructs of the IMB model are likely applicable to this population, unique content and situational factors that influence adherence information, motivation, and behavioral skills among HIV+ MU-MSM have not been empirically determined. Moreover, no technology-based ART adherence interventions specifically tailored to the needs of HIV-positive MSM have been conducted. To address these theoretical and intervention gaps, we propose a four-phase study. In Phase 1, four online focus groups will be conducted to fully explicate the IMB model for HIV+ MU-MSM and to adapt IMB-related adherence measures for the target population. The goal of Phase 2 is to measure, characterize, and evaluate ART adherence in HIV+ MU-MSM and the adapted IMB model of ART adherence developed in Phase 1. HIV+ MU-MSM (n=209) will be recruited online to participate in a survey of ART adherence, the adapted IMB-related measures, substance use, and empirically derived determinants of poor adherence (e.g., depression). In addition, participants will report their technology use and preferences for smart phone application content to inform intervention development. Phase 3 is to develop and conduct usability testing on the smart phone application ART adherence intervention tailored for HIV+ MU-MSM. Intervention components will consist of tailored informational messages, a motivational personal intervention guide, medication reminders and monitoring, self-reflection and strategy rehearsal. The intervention will be usability tested among five participants prior to finalizing the look and content. The smar phone application ART adherence intervention will be pilot tested among HIV+ MU-MSM in Phase 4. HIV+ MU-MSM randomized to the experimental group will participate in the smart phone application intervention for 60 days. Adherence levels of the experimental (n=30) and treatment-as-usual control (n=30) groups will be compared at baseline, post-intervention, and 2 months. Process (e.g. days per week accessing the intervention, overall retention), as well as user acceptability and satisfaction, measures will be collected throughout the study period. The primary significance of the proposed research to public health is to improve ART adherence among substance-using populations and reduce rates of HIV transmission among men who have sex with men. If found effective, the intervention could be scaled-up rapidly for dissemination and adapted to other substance-using populations.